The core of the present invention resides in the area of sealing packaging containers made from a packaging laminate. Sealing then refers to the closing of an open end of the packaging container. This “open end” will be the end which will form the top of the packaging container.
Though not forming any part of the present invention it may be worthwhile to mention a few words of the packaging laminate. The packaging laminate generally comprises a core of fibre material, a paper board, sandwiched between additional layers for providing further beneficial properties. These additional layers may comprise thermoplastic layers forming a barrier against liquid, and to some extent to gases, such as oxygen, and aluminium layers forming a barrier against light and gases, again oxygen may be mentioned as an example. Further layers may include adhesives etc. The field of packaging laminates is well explored and new packaging laminates emerge regularly. A relatively common feature is that packaging containers made from such a packaging laminate are sealed with the aid of an outermost plastic layer of the packaging laminate. Starting from a sheet or web of packaging material a sleeve or tube is formed by fusing two opposing edges of the sheet or web. The fusing is performed in the same way as the sealing, i.e. by heating the outermost plastic layers in the areas to be sealed followed by pressing the areas towards each other. It may be noted that the “outermost layer” is meant to designate an outermost layer of the packaging laminate as such, and for a sheet of packaging laminate there are generally two layers being the “outermost layer”; one on each side of the sheet. Furthermore, the outermost layer may obviously be located on the interior side of a packaging container folded from the packaging laminate.
Referring back to the heating and pressing, the order of events may be shifted such that the pressing is started before the heating. Common heating methods are heating with a flow of hot air, heating by ultrasonic radiation (basically friction), and induction heating. Numerous publications disclose details of various heating techniques, various packaging laminates and so forth.
The thus formed sleeve is sealed in one end, commonly by using one of the techniques mentioned, after which it if filled with a product and sealed at the remaining open end. Depending on the type of packaging container there are different techniques that are used.
The text passages above have the purpose of giving a brief introduction to the technical field within which the present invention resides and the information is considered well-known to the skilled person.
The present invention is associated with the narrow area of heating the packaging laminate prior to sealing one end thereof, and though the advantages were discovered in connection to one particular type of packaging container the invention as such may be used in relation to other packaging containers where it is suitable.
The particular type of packaging container mentioned is a gable-top container. This type of packaging container is well-known since almost a century and still commonly used. There is an abundance of publications relating to gable-top containers, yet in a few words the gable-top container is formed from a packaging laminate blank, i.e. a rectangular piece of packaging material. The blank is creased or scored to facilitate folding, and two opposing edges are sealed together in this case called 5. Panel for formation of a sleeve, a flattened sleeve to be more exact, still having an open top end and an open bottom end (top and bottom referring to the function of the ends in relation to a finished packaging container. The thus formed sleeve is fed to a filling machine in this flattened state, and in the filling machine the flattened sleeve is risen to a sleeve having a square or rectangular cross section, after which it is arranged on a mandrel of a mandrel wheel. While on the mandrel wheel the bottom end of the sleeve is heated by means of hot air and sealed by folding the open bottom end according to a particular bottom configuration, of which there are several to choose from. This partly formed packaging container is removed from the mandrel and is arranged on a conveyor with the top end directed upwards, and while arranged on the conveyor the packaging container is sterilized and filled. After filling the still open end of the packaging container is to be sealed, and since we are now closing in on the particular field of the present invention this step will be described in some more detail. When sealing the bottom end the folded end is pressed with great force against an anvil (on the mandrel) and an adequate seal is accomplished with relative ease. The top end is a bit more delicate, since the top end has to be properly sealed while still providing an opening for pouring out the product. Such opening may a separately provided plastic closure arranged in or on a hole configuration on one of the gable panels yet the opening may also be provided by a consumer tearing apart a specific part of the sealed area in the top end, in a manner well-known for anyone having opened a gable-top container before the time of plastic closures.
The edges to be sealed are heated by means of a delicately designed nozzle, and the flow of hot air is dependent on the type of material of the packaging laminate, the type of opening device to be arranged etc. There are several examples of such nozzles in the literature, one example including EP0526069 by the present applicant. Each nozzle is tailor made for its purpose, e.g. individually designed in relation to a particular package size, a particular top configuration, a particular closure, etc.
The present invention relates to an improved heating nozzle arrangement.